Operational mode control of a motor

ABSTRACT

One example is a system for controlling a motor during startup. The system includes measurement logic, pattern detection logic, and mode logic. The measurement logic monitors a back-electromotive force (BEMF) signal representing a BEMF of an electric motor and the pattern detection logic monitors this signal to detect instances of the monitored BEMF signal exhibiting a predetermined pattern. The mode logic enables control of the electric motor according to a plurality of modes of control. In some examples, the mode logic initially employs a first mode of control and switches from the first mode of control to a second mode of control in response to the pattern detection logic detecting that a BEMF signal exhibits the predetermined pattern over a plurality of commutation states.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/704,149 filed on Dec. 5, 2019, which is a continuation of U.S. patentapplication Ser. No. 16/009,534, filed Jun. 15, 2018, now U.S. Pat. No.10,523,144, each of which is incorporated herein by reference in itsentirety.

TECHNICAL FIELD

This disclosure relates generally to the operational mode control of amotor.

BACKGROUND

Various types of electrical motors may need to transition betweenoperational modes. For example, block-commutating permanent magnetsynchronous motors (PMSMs) may begin operation in a first mode (e.g., anopen-loop initialization mode) where forced commutation is used and astator generates a rotating magnetic field that begins to rotate a rotorat low speeds. Once the rotor achieves a sufficient speed, a controllerand/or switch may have the PMSM switched from the first-mode(initialization mode) to a second-mode that may be referred to asclosed-loop or sensorless operating mode.

SUMMARY

One example is a system that includes measurement logic, patterndetection logic, and mode logic. The measurement logic measures aback-electromotive force (BEMF) signal representing a BEMF of anelectric motor. The pattern detection logic detects instances of themonitored BEMF signal exhibiting a predetermined pattern. The mode logicenables control of the electric motor according to a plurality of modesof control. The mode logic initially employs a first mode of control andswitches from the first mode of control to a second mode of control inresponse to the pattern detection logic detecting that a BEMF signalexhibits the predetermined pattern over a plurality of commutationstates.

Another example is a method. The method includes measuring backelectromotive force (BEMF) signals of a motor during each of a pluralityof commutation states of the motor. The method also includes detectingone-or-more periodic characteristics associated with aback-electromotive force signal (BEMF signal) during each of theplurality of commutation states of the motor. The motor also includesswitching the motor from a first control mode to a second control modein response to detecting that the predetermined pattern occurs in aplurality of consecutive commutation states.

An example system includes sensor circuitry to provide a measure of theback electromotive force (BEMF) for a floating phase of a multi-phaseelectric motor. A controller has outputs to provide control signals tocontrol operation of the multi-phase electric motor. The controller isconfigured to utilize a non-BEMF based first mode of control toinitially control the multi-phase electric motor. The controller is alsoconfigured to detect each occurrence of a pattern in the sensor signalthat includes crossing a predetermined signal value during a selectedcommutation state of the multi-phase electric motor. The controller isfurther configured switch from the first mode of control to a BEMF-basedmode of control in response to detecting occurrences of the pattern overa plurality of consecutive commutation states.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example system to control switching betweendifferent control modes of an electric motor.

FIG. 2 illustrates an example of a motor circuit.

FIG. 3 is a graph showing an example of back-electromotive-force (BEMF)voltage waveforms over a plurality of commutation states.

FIG. 4 is a graph illustrating an example BEMF waveform for a givenphase over multiple commutation states.

FIG. 5 is a graph of example BEMF waveforms for multiple phases over aplurality of commutation states.

FIG. 6 is a graph illustrating an example BEMF waveform for a givenphase over multiple commutation states lacking stability to change thecontrol mode for a motor.

FIG. 7 illustrates an example of a motor system.

FIG. 8 illustrates an example flow diagram of a method to controlswitching between control modes of a motor.

FIG. 9 illustrates another example flow diagram of a method to controlswitching between control modes of a motor.

DETAILED DESCRIPTION

This disclosure provides systems and methods to switch an electric motorfrom an initialization mode to a closed-loop (e.g., sensorless) mode.

By way of example, a system may measure the back-electromotive-force(BEMF) (e.g., BEMF voltage) of one or more phases of an electric motor(e.g., a three-phase permanent magnet synchronous motor (PMSM)). Inresponse to recognizing a predetermined signal pattern in the BEMFvoltage, the motor may be switched from an initial, low speed controlmode to a closed-loop control mode. For example, during low-speed,open-loop control, a motor controller or other circuitry may monitor andevaluate the BEMF signals for a given current speed and/or referencecurrent for the motor. If the predetermined pattern is not detected atthe given speed and/or reference current, the speed and/or referencecurrent signals may be increased (e.g., incrementally) during theinitial open-loop control mode for additional evaluation of the BEMF.The BEMF thus may be monitored to detect the pattern in each commutationstate while changing the speed and/or current parameters of the motorduring the open-loop control mode until the predetermined BEMF patternis detected over a plurality of commutation states. For example, thepredetermined pattern may correspond to the BEMF signal crossing apredetermined voltage (e.g., a midpoint or zero crossing) during aselected commutation state for a given phase (e.g., while the phase isfloating). Once the pattern of crossings is detected over a number ofcommutation states, which itself may constitute the predeterminedpattern, the motor controller or other circuitry may automaticallytransition operational control from the initial (e.g., open-loop)control to closed-loop control (e.g., BEMF-based, sensorless control).

FIG. 1 illustrates an example of a motor control system 100 configuredto control a motor 101. The system 100 includes logic (e.g., implementedin a motor controller) that is configured to switch between operationalmodes of an electric motor. For example, during start-up of the motor,the system 100 enables automatic transition between low-speed, open-loopcontrol and BEMF-based, sensorless control at higher speeds ofoperation. The example system 100 includes measurement logic 104,pattern detection logic 106, mode logic 108, and control logic 112. Thecontrol logic 112 is coupled to a driver 116 that is configured tosupply electric current to phase windings of the motor 101 in responseto control signals provided by the control logic 112. In some examples,some or all of the logic may be fabricated as part of a motor controllerimplemented on a common substrate (e.g., integrated in a common chip ordie). For example, the control system 100 and its logic blocks may beimplemented as hardware on a silicon chip, in an integrated circuit, ina field-programmable gate-array (FPGA), with discreet logic devices. Inother examples, the logic may be implemented in an arithmetic logic unit(ALU), which may be a standalone ALU or within a processor core. Thus,the functionality implemented by the logic in the motor control system100 may be implemented in a variety of ways.

In one example, the measurement logic 104 includes voltage measurementcircuitry configured to measure the BEMF for each phase of the motor 101such as via one or more connections 102. While in the example of FIG. 1,the measured signals are shown received via line(s) 102 from the motor,such signals alternatively may be measured by sensing voltages from thedriver 116 via corresponding sensing circuitry. The measurement logic104 is configured to measure BEMF signal voltages provided by each phaseof the motor 101 and provide the measurements to the pattern detectionlogic 106 for subsequent processing. In some examples, the measurementlogic 104 may implement digital processing of measured signals forfurther evaluation by the pattern detection logic 106.

As a further example, the measurement logic 104 periodically samples theBEMF signals at a sample rate, such as with an analog-to-digitalconverter (ND converter) that converts the BEMF signals into digitaldata for further analysis by the pattern detection logic 106. Signalsconverted from analog to digital data can include BEMF voltage signalsgenerated by each floating phase of the motor 101. In an examplethree-phase PMSM, only two phases conduct current at any time, leavingthe third phase floating, which depends on the current commutationstate. The measurement logic 104 thus may take several (e.g., periodic)measurements of the BEMF signal of a respective floating phase as thatsignal travels through one or more commutation periods of the motor 101.The measurements of the BEMF signal from each floating phase thus ismeasured and provided to the pattern detection logic 106.

The pattern detection logic 106 receives, as inputs, measurements of theBEMF signals provided by the measurement logic 104 over time. Thepattern detection logic 106 is configured to detect instances of themonitored BEMF signal exhibiting a predetermined pattern. In response todetecting the predetermined pattern, the pattern detection logic 106 mayenable (or instruct) the mode logic 108 to switch from an initial (e.g.,open-loop) mode of control to a different (e.g., closed-loop) mode ofcontrol.

For example, the pattern detection logic 106 is configured to identifyeach instance of the predetermined pattern based on the measured BEMFsignal (e.g., from measurement logic 104) crossing a predeterminedsignal value during a selected commutation state of the electric motor101. An example predetermined voltage is zero volts (e.g., a zerocrossing) for a floating phase of the motor, although other voltagelevels may be used. In some examples, the pattern detection logic 106may detect that the predetermined pattern (e.g., zero crossing) occursin each a plurality of consecutive commutation states. For instance, thepattern detection logic 106 may count a number of consecutive validcrossings that occur and store the count value in memory. The patterndetection logic 106 may reset the count value in response to detectingthat the BEMF signal does not exhibit the predetermined pattern duringany of the plurality of commutation states. The mode logic 108 thus maymonitor or receive the count value to control whether or not to switchto the next control mode, as disclosed herein. In other examples, thepattern detection logic 106 may utilize additional or different patternsbased on various signals or other characteristics that are useful fordetermining when it is desirable to switch the mode of the motor 101. Asyet another example, the measurement logic 104 and pattern detectionlogic 106 may be implemented as hardware, such as a comparator tocompare the measured BEMF voltage for each phase relative to a voltagethreshold (e.g., a mid-point of the BEMF voltage).

The mode logic 108 is configured to control an operating mode of theelectric motor 101 according to one of a plurality of modes of control.For example, the control modes can include a non-BEMF based control modeduring low speeds and a closed-loop (e.g., sensorless) control mode athigher speeds. For example, the control mode for low speeds may utilizeopen-loop or closed-loop control and a BEMF-based control may be usedfor higher speeds. The mode logic 108 thus may switch between itscontrol modes based on pattern detection information determined by thepattern detection logic 106. For example, the mode logic 108 isconfigured to initially (e.g., during start up) employ open-loop controland switch from such open-loop control to a closed-loop control inresponse to the pattern detection logic 106 detecting that BEMF signalsexhibit the predetermined pattern over a plurality of commutationstates, such as disclosed herein. As an example, the mode logicimplements a state machine that transitions between control modes basedon detecting (or not detecting) a pattern in the BEMF signals.

Control logic 112 is configured to set speed and/or current applied tothe electric motor 101. For example, the control logic 112 is coupled toinputs of the driver 116, such as to supply PWM signals to switchdevices (e.g., transistors) that are activated and deactivated to supplyelectric current to phase windings of the motor 101 according to acommutation state of the motor. The control logic 112 thus implements amode of control (e.g., low-speed or closed-loop control) based oninstructions from the mode logic 108. The control logic 112 mayimplement a cascaded control using speed and current or use only speedor only current during low speed control of the motor 101.

As an example, during the first mode of control (e.g., during start upat low speeds), in response to detecting that the BEMF signal fails toexhibit the predetermined pattern during at least one of the pluralityof commutation states, the control logic 114 adjusts speed and/orcurrent applied to the electric motor. For example, the control logic114 incrementally adjusts (e.g., increases) speed and/or current appliedto the electric motor 101 over consecutive time intervals during thefirst operating mode until the pattern detection logic 106 detects thepredetermined pattern in a series of consecutive commutation states. Asmentioned, the mode logic 108 switches from the first (e.g., non-BEMF)mode of control to the second (closed-loop) mode of control based on thepredetermined pattern being detected in a series of consecutivecommutation states of the motor. The control logic 112 uses the mode ofcontrol (e.g., established by mode logic 108) as well as the speedand/or reference current setting to implement corresponding control ofassociated drive circuitry.

The control logic 112 provides control signals to the drive circuitry116 for controlling the motor 101 based on the control mode determinedby the mode logic 108. The drive circuitry 116 thus supplies current forexciting windings of the motor 101 based on control signals from thecontrol logic 112. For example, as shown in FIG. 2, the drive circuitry116 may include an H-bridge or other drive arrangement of switch (e.g.,transistor) devices configured to supply current to respective pairs ofwindings based on control signals from a motor controller that includesthe control logic 112.

Unlike other approaches for transitioning from open to closed-loopcontrol, the systems and methods disclosed herein do not require apre-defined motor speed or a motor current threshold. Rather, theoperating mode transition occurs according to the BEMF voltages of themotor 101 as well as other useful/desirable operating conditions and/orsystem parameters. For example, at low motor speeds, the BEMF's signalto noise ratio (SNR) is too low to be used for BEMF sensor-lessclosed-loop motor control and this causes the rotor position detectionto be unreliable. Thus, at low speeds, operation of the motor isgenerally limited to non-BEMF speed control (e.g., open-loop or forcedcommutation) that exhibits degraded performance compared to closed-loopspeed control at higher speeds. However, as disclosed herein, the system100 of FIG. 1 determines when the BEMF signal is sufficiently stable, bydetecting a predetermined pattern in the BEMF signals, to switch to aclosed-loop mode of control, such as a BEMF-based sensorless,closed-loop mode of control. In other examples, the control maytransition from closed-loop (e.g., low speed, non-BEMF-based control,which may be sensorless or employ sensors) to another closed-loop modeof control (e.g., BEMF-based sensorless control). The type of non-BEMFbased control implemented at lower speeds can vary depending onapplication requirements.

FIG. 2 illustrates an example of a motor system 200. The motor system200 includes a driver 202 that is coupled to motor 204, demonstrated asa three phase motor having phase windings A, B and C. In the example ofFIG. 2, the phase windings A, B and C each has an inductance shown asL1, L2 and L3, respectively. As one example, the motor may be a PMSMthat includes three non-permanent electromagnetically activated magnets(electromagnets) mounted in its stator/housing and may have fourpermanent magnets mounted to its central rotator. However, other examplemotors may be employed in the examples herein with these other examplemotors having different numbers of permanent magnets and electromagnets.For example, the three electromagnets of the stator may be activatedwith six commutation states that work in pairs to generate the phasevoltages (three-phased power supply) to rotate the motor.

The driver 202 includes an arrangement (e.g., H-bridge) of switchdevices S1, S2, S3, S4, S5 and S6 (e.g., transistors, such asfield-effect transistors or bipolar junction transistors). A motorcontroller 206 (e.g., corresponding to control system of FIG. 1) iscoupled to control the switches of the driver 202 to generate outputphase voltages V_(A), V_(B), and V_(C) which are generally out-of-phasefrom each other (e.g., by 120 degrees). In this example, there are threeupper switches S1, S3, and S5 connected to a high voltage supply V+ andthree lower switches S2, S4, and S6 connected to a low (e.g., ground)voltage. The upper switches S1, S3, and S5 and the lower switches S2,S4, and S6 work in conjunction to supply current to the phase windings,which generate corresponding phase voltages V_(A), V_(B), and V_(C). Asdisclosed herein, the motor controller 206 is configured toautomatically switch the PMSM from an initialization mode (e.g.,implementing open-loop or forced commutation control) to a run mode(e.g., closed-loop control) based on BEMF signals exhibiting aprescribed pattern. If appropriate, other signals and operatingparameters associated with the motor operation may be utilized as partof the determination to change modes of control. The motor controller206 may utilize the same BEMF signals, which are monitored to controltransition between control modes, to sustain the motor 101 in the runmode during normal (high-speed, BEMF-based sensorless) operation. In atleast some examples, the motor controller 206 supplies control signalsto switches S1-S6 in a prescribed order in order to generate the threephase voltages (V_(A), V_(B), and V_(C)) to power the electromagnets inthe stator that effect desired movement of the rotor.

FIG. 3 is a graph 300 illustrating various example ideal waveforms of amulti-phase motor, such as motor 101 or 204. FIG. 3 illustrates phasevoltages for phases A, B and C at different rotor electrical positionsand associated commutation states (e.g., six commutations states of 60electrical degrees each). In some examples of motor control, PWM signalsmay drive switches S1-S6 (FIG. 2) on and off to generate the respectivephase voltages V_(A), V_(B), and V_(C). In this example, each of thephase voltages exhibits a crossing of a predetermined voltage (e.g.,midpoint or zero crossing) centered near a selected commutation state,as respective floating phases ramp up or down.

FIG. 4 is a graph 400 illustrating an example phase voltage 404 for agiven phase of a motor (e.g., motor 204) superimposed over motorcommutation states 402. Additional phase and BEMF signals for differentphases could have been graphed in FIG. 4 with other signals (see, e.g.,FIG. 5); however, for the sake of clarity a single phase voltagewaveform 404 is shown in the example of FIG. 4. As shown, during itsfloating phase, the phase voltage 404 decreases from its energized,high-voltage state (e.g., near about 2 V) to its low voltage state(e.g., about 0 V). The decreasing portion of the phase voltagecorresponds to a BEMF generated for the given phase (during floating).In this example, the BEMF voltage crosses a predetermined voltage (e.g.,a midpoint of about 1 V) that meets stability criteria. For example, thestability criteria includes the BEMF voltage having a zero or otherpredetermined crossing during a selected commutation state, which may bedetected (e.g., by pattern detection logic) during the floating phase ofthe selected commutation state.

As disclosed herein, the measurement logic 104 (FIG. 1) measures theBEMF voltage waveform 404 during commutation states. When themeasurement logic 104 measures the BEMF voltage of the phase voltage404, the phase winding is floating (e.g., non-energized), such that theBEMF voltage waveform 404 decreases from its high to its low voltageamplitude. In the example of FIG. 4, the crossing is demonstrated tooccur at point 412 (e.g., about 1V), which is valid crossing for thefloating phase since it occurs during the selected commutation state(state 1 in this six commutation state example), indicated at 402′. Themeasurement of BEMF voltage for each phase (e.g., by measurement logic)may be triggered by commutation states when each respective phase isdetermined to be floating. As illustrated in FIG. 4, this may occurduring a time interval of a respective commutation state 402′. Inparticular, the midpoint (e.g., zero) crossing of the BEMF voltage forthe given phase, demonstrated at 412, may occur at an intermediateportion of the floating phase during commutation state 402′. The patterndetection logic is configured to detect each occurrence of the BEMFvoltage crossing the predetermined voltage (e.g., valid crossings) foreach phase of the motor.

As shown in FIG. 4, the crossing point 412 may further be determined (bypattern detection logic) to be a valid crossing if it occurs within arange of the midpoint or at a midpoint value. In some examples, thecrossing point 412 may be also determined to be a valid crossing if itoccurs at any time within the commutation period or within a prescribedtime interval at or near a center of such commutation period. In thisway, the pattern detection logic can condition the validity of a BEMFcrossing as having both a component of voltage (e.g., crossing apredetermined voltage, such as zero) and a component of time (e.g.,synchronized with a prescribed commutation state), which conditions arerepresented within a box 413 in FIG. 4. As discussed below, each of theother phase BEMF signals may be evaluated (by pattern detection logic)in combination with those of example FIG. 5 to determine that theexistence of a pattern, including valid crossings, occurs over aplurality of consecutive commutation states for the motor.

FIG. 5 illustrates an example graph 500 of each of a plurality of phasevoltages 504, 505 and 506 superimposed on commutation state signal 502.In the example of FIG. 5, the phase voltages 504, 505, 506 provide BEMFsignals that cross predetermined voltage values (e.g., zero crossings),shown at 510, 512 and 514 during the corresponding commutation state foreach respective floating phase. Accordingly, by detecting such patternin the BEMF voltages signals over a series of commutation states, amotor controller can determine the operation of the motor system issufficiently stable and switch from its closed-loop control to itsopen-loop control.

FIG. 6 illustrates an example graph 600 that depicts a commutation statesignal 602 and a given phase voltage signal 604, similar to FIG. 4. Inthis example, the BEMF voltage transitions from a high voltage level toa low voltage value. However, in this example, the crossing of thepredetermined voltage (e.g., zero crossing) does not occur during anexpected commutation state for the floating phase. Instead, the crossingoccurs in a subsequent commutation state of the motor, such that thecrossing is not a valid crossing for purposes of pattern detection toenable switching the motor from the first-mode (e.g., open loop Lowspeed) to the second-mode (e.g., closed loop BEMF Sensorless). Forexample, arrows 608 generally indicate areas where the phase voltagesignal 604 continues to increase during its expected floating phaseperiod such that the threshold crossing occurs during a wrongcommutation state. The example motor represented by the signals of FIG.6 can be similar a motor discussed above that implements six commutationstates for a block-commutated motor. The magnitude (or predeterminedmagnitudes) of BEMF voltage signal is dependent on motor frequency/speedand a supply voltage.

FIG. 7 illustrates an example of a motor system 700 that includes amotor controller 710 configured to implement logic that controls anelectric motor 701. For example, the motor 701 may be a multi-phase(e.g., three-phase) PMSM, such as a brushless DC motor exhibitingtrapezoidal or sinusoidal BEMF signals. In the example of FIG. 7, themotor controller 710 includes measurement logic 704, pattern detectionlogic 706, mode logic 708 and control logic 714. In other examples, themeasurement logic 704 and associated phase sensing circuitry (not shown)could be implemented external or internal of the motor controller 710.

As disclosed herein, the measurement logic 704 receives BEMF signals foreach phase of the motor 701 via one or more input connections 703. Themeasurement logic 704 may include voltage measurement circuitry thatsupplies the measured BEMF voltage signals to pattern detection logic706, such as disclosed herein. In this example, the pattern detectionlogic 706 includes crossing detection logic 716 and a counter 718. Thecrossing detection logic 716 can detect each occurrence of the measuredBEMF signal for a floating phase crossing a predetermined value (e.g., 0V) during a corresponding commutation state of the motor, such asdiscussed above. For example, crossing detection logic 716 detects azero or midpoint crossing of the BEMF signal for a given phase decreasefrom its positive to a negative voltage values during a commutationstate while the given phase is floating.

The pattern detection logic 706 may also control the counter 718 tocount each consecutive occurrence that the measured BEMF signal crossesthe predetermined value (e.g., zero crossing). For example the counter718 includes a counter value 719 tracking the number of times that theprescribed pattern of the BEMF occurs during consecutive commutationstates. The counter 718 can store the counter value 719 in a register, amemory location, or similar location that is accessible by the patterndetection logic 706. The counter 718 further may be configured to resetthe counter value in response to the crossing detection logic 716detecting that the BEMF signal does not cross the predetermined valueduring one or more of the commutation states.

The mode logic 708 may be configured to operate similar to the modelogic 108 of FIG. 1. For example, the mode logic 708 is configured toswitch between two or more control modes for the motor 701 based on thecounter value 719, which can be accessed by or provided to the modelogic 708 by the pattern detection logic 706. For example, the modelogic 708 (and/or pattern detection logic 706) may compare the countervalue 719 to predetermined threshold that establishes the number ofconsecutive zero crossings needed to switch from open-loop control toclosed-loop control. The threshold may be a default value or beuser-defined (e.g., programmable). As one example, the counter thresholdmay be set based on (or at) the number of commutation states that occurover 360 electrical degrees of the motor. In response to determining toswitch between modes of operation, the mode logic 708 can provide a modechange command to the control logic 714.

The control logic 714 provides control signals to a driver 724 to applycorresponding current to phases of the motor 701. The control signalsdepend on speed and/or current values that the control logic sets formotor control. The control logic 714 may be implement open-loop control720 or closed-loop control 722 depending on the mode of controlestablished by the mode logic 708. During start up, while the motor isoperating in its open-loop control operating mode, the control logic 714incrementally adjusts the speed and/or current applied to the motor 701over time. The incremental increase in speed and/or current may continueover time during the closed-loop control mode until the patterndetection logic 706 detects the predetermined pattern in a series ofconsecutive commutation states. For example, if the pattern is notdetected during the series of consecutive commutation states or apredetermined time interval elapses, the control logic 714 incrementsthe speed and/or current applied to the motor. Once the predeterminedpattern is detected a threshold number of times in a series ofconsecutive commutation states, the mode logic 708 commands the controllogic 714 to switch from the open-loop control 720 to the closed-loopcontrol 722. The control logic 714 can further adjust at least one ofthe speed and/or current applied to the electric motor 701 in responseto detecting that the BEMF signal fails to exhibit the predeterminedpattern during at least one of the plurality of commutation states. Insome examples, however, the pattern detection logic 706 may continue tolook for the predetermined pattern in a series of consecutivecommutation states and thereby control switching between the respectivemodes of control 720 and 722 being implemented by the control logic 714.

In view of the foregoing structural and functional features describedabove, example methods will be better appreciated with reference toFIGS. 8 and 9. It is appreciated that the methods are not limited by theillustrated order. Some actions could occur, in other examples, indifferent orders and/or concurrently from that shown and describedherein. Moreover, not all illustrated features may be needed toimplement a method. For example, each of the methods of FIGS. 8 and 9may, in some examples, be implemented in a motor controller to control amotor similar to as described above with reference to FIGS. 1-7.

FIG. 8 illustrates an example method 800 of controlling run modes foroperating an electric motor 101. At 802, back electromotive force (BEMF)signal(s) of a motor are measured. For example, the BEMF signal(s) maybe periodically measured during each of a plurality of commutationstates of the motor. These measurements may be performed by measurementlogic 104 or 704. Additionally, the first control mode may be maintaineduntil the method 800 determines (as discussed below) that thepredetermined pattern occurs in each of a plurality of consecutivecommutation states.

The method 800 detects, at 804, occurrences of a predetermined patternin the BEMF signal during each of the plurality of commutation states ofthe motor. In some examples, the detections may include periodicdetections of one-or-more characteristics associated with the BEMFsignal during each of the plurality of commutation states of the motor.For example, the detection may be performed by pattern detection logic106 or 706.

At 806, the motor 101 is switched from a first control mode to a secondcontrol mode in response to detecting that the predetermined patternoccurs in a plurality of consecutive commutation states. This switchingof the control modes thus is performed by control logic based on a modedetermined by the mode logic, such as disclosed herein. In someexamples, the method 800 includes counting a number of times the BEMFsignal crosses a predetermined value during each of the respectivecommutation states. A counter may be reset in response to detecting thatthe BEMF signal for a floating phase does not cross the predeterminedvalue during one of the commutation states. The motor may be switchedfrom the first control mode to the second control mode if the counter isdetermined (e.g., by comparator) to have a count value that satisfies apredetermined threshold value.

For example, the electric motor may be operated in the second controlmode (e.g., closed-loop operating mode) using a trapezoidal BEMFtechnique. Thus, the method 800 may automatically switch from the firstoperating mode to the second operating mode without interaction from anexternal actor, and without requiring a pre-defined motor speed or amotor current threshold. The approach disclosed herein is applicable todifferent types of motors and control schemes.

In some further examples, the method 800 may control at least one ofspeed or current applied to the motor. This can be performed byadjusting at least one of speed or current applied to the motor during afirst mode of control in response to detecting that the BEMF signalfails to exhibit the predetermined pattern during at least one of theplurality of commutation states. The detecting and the switching may berepeated based on speed and/or current being applied to the motor, whichspeed and/or current may be adjusted over time.

FIG. 9 illustrates another example of a method 900 of controlling anelectric motor 101, including switching between modes of control (e.g.,between low-speed open-loop control and BEMF-based sensorless control).The method 900 begins, at 902, by initializing a motor. In someexamples, the required motor initialization may be performed by a motorcontrol logic similar to the control logic 112 of FIG. 1. Thisinitialization may include starting the motor in a forced commutationmode, ramping up its commutation frequency until a minimum motorrotational speed is reached, and increasing the motor speed so as tobegin generating BEMF signals. Once such speed is reached, the method900 may proceed to 904.

At 904, a one or more one or more signals are evaluated for apredetermined signal pattern. For example, the signals being evaluatedinclude BEMF waveforms for the respective phase windings in eachcommutation state. This checking may be performed by pattern detectionlogic (e.g., logic 106 or 706). For example, logic monitors anddetermines if a BEMF signal characteristic occurs, such as whether azero crossing of one or more BEMF signals is present during a respectivecommutation period. In some examples, after or concurrently with 904, at906, a determination is performed to determine if an overcurrentcondition has occurred regarding the motor. If so, the motor 101 isplaced into a fault condition (e.g., safe state), at 908, and, after apredetermined time the motor is switched, at 910, to its initial forcedcommutation frequency and the method returns to 902. A motor controllogic (e.g., logic 112 or 714) may place the motor 101 into this faultcondition.

If an over current condition was not detected at 906, then adetermination is made as to if a pattern was recognized, at 912. Logicsuch as the pattern detection logic 106 or 706 discussed above withreference to FIG. 1 may perform the determination at 912 and maycontribute to determining if a predetermined pattern was recognized(detected). As disclosed herein, the pattern may correspond to apredetermined BEMF signal pattern in which one or more BEMF voltagesignals cross a predetermined voltage (e.g., zero crossings) during oneor more commutation states. In some examples, the predetermined BEMFsignal pattern corresponds to detecting each of the BEMF voltage signalscrossing a predetermined voltage (e.g., zero crossings) during aplurality of consecutive commutation states. For each detection of thepredetermined pattern, a count value is incremented to track each validcrossing. If the pattern is not recognized during a commutation state,then the count value is reset, at 914, and a current driven to the motoris adjusted. For example, the current may be adjusted by using anincremental up or down current amperage. Thus, while the signal doesn'tmatch the expected pattern, the reference current and/or speed values inthe open-loop control are changed after a certain number ofcommutations. From 914, the method returns to block 904.

If there is a recognized pattern at 912, then a determination is made,at 916 as to if the pattern was recognized “N” (a threshold) number oftimes. For example, a counter (e.g., counter 718) may provide acorresponding counter value to represent the number of valid crossingsdetected over a series of commutation states. If the pattern is notrecognized at 916, then the method returns to block 904. In response todetecting the predetermined pattern, at 916, “N” number of times, themethod proceeds to 920 where a control mode of the motor may be changed.For example, the mode change at 920 can correspond to switching from anopen-loop (e.g., forced commutation) control mode to a closed-loop(e.g., BEMF-based sensorless) control mode. As mentioned, the mode logic108, 808 discussed above may be provided information as to whether thepattern was recognized “N” times to enable switching between respectivemodes as disclosed herein. In one example, “N” may be set to N≥6, whichwould reflect two detections per phase in a three-phase motor. In otherexamples, different values of “N” may be used. Additionally, oralternatively, the value of “N” may be set to a default value (e.g.,N=6) or be user programmable (e.g., a register entry set in response toa user input).

In view of the foregoing, employing the above description and figuresexplained example systems and methods that may eliminate a lengthymanual tuning to find a minimum speed and current needed to generate runtime signal(s) from the a motor that can include the BEMF signal(s).Eliminating manual tuning enables faster time to market andapplicability to a variety of different motor configurations andoperating conditions. Unlike implementations that may use previouslychosen speed and current values that were fixed and specific to themotor and load conditions, the approach herein affords automatic modechanges that increase system robustness and flexibility.

What have been described above are examples of the disclosure. It is, ofcourse, not possible to describe every conceivable combination ofcomponents or method for purposes of describing the disclosure, but oneof ordinary skill in the art will recognize that many furthercombinations and permutations of the disclosure are possible.Accordingly, the disclosure is intended to embrace all such alterations,modifications, and variations that fall within the scope of thisapplication, including the appended claims.

What is claimed is:
 1. A method comprising: receiving, by patterndetection logic, a signal generated by a motor having a plurality ofcommutation states and operating in a first control mode; determining,by the pattern detection logic, a predetermined signal pattern in thesignal generated by the motor; incrementing, by the pattern detectionlogic, a count value based on a number of times over a set of theplurality of commutation states that the predetermined signal pattern isdetermined in the signal; and in response to the count value exceeding acount threshold, selecting, by the pattern detection logic, a secondcontrol mode to operate the motor.
 2. The method of claim 1, wherein:the signal comprises a back-electromotive force (BEMF) signal; and thesignal corresponds to the BEMF signal crossing a predetermined voltageduring a selected commutation state of the plurality of commutationstates.
 3. The method of claim 1, further comprising: initializing, by amotor control logic, the motor, wherein the initializing includesstarting the motor in the first control mode and increasing acommutation frequency of the motor from a first commutation frequencyuntil the motor generates the signal.
 4. The method of claim 3, furthercomprising: determining, by the motor control logic, whether anovercurrent condition with the motor exists.
 5. The method of claim 4,further comprising: in response to the overcurrent condition existingwith the motor, placing, by the motor control logic, the motor in afault condition.
 6. The method of claim 5, further comprises: inresponse to placing the motor in the fault condition, switching, by themotor control logic, the motor to the first commutation frequency. 7.The method of claim 3, further comprising: in response to determiningthe predetermined signal pattern is not determined in the signal,resetting the count value; and increasing, by the motor control logic,the commutation frequency.
 8. The method of claim 1, wherein: the countthreshold is set in response to a user input.
 9. The method of claim 1,further comprising: sampling, by a measurement logic, the signalperiodically; and converting, by the measurement logic, the signal intoa digital signal.
 10. The method of claim 9, wherein: the samplingincludes a plurality of measurements of the signal of a respectivefloating phase of one or more commutation periods of the motor.
 11. Asystem comprising: measurement logic operable to measure a signalassociated with a motor having a plurality of commutation states;pattern detection logic operable to: receive the signal; compare thesignal to a predetermined signal pattern; based on the comparison,increment a count value; and in response to the count value exceeding acount threshold, generate a motor control selection to switch operationof the motor from a first control mode to a second control mode; andmode logic operable to: receive the motor control selection; and operatethe motor based on the motor control selection.
 12. The system of claim11, wherein the measurement logic is operable to: measure the signalperiodically.
 13. The system of claim 11, wherein: the signal comprisesan analog signal; and the measurement logic is operable to convert theanalog signal to a digital signal.
 14. The system of claim 11, whereinthe measurement logic is operable to: measure the signal for arespective floating phase as the signal travels through one or morecommutation periods of the motor.
 15. The system of claim 11, wherein:the pattern detection logic includes a comparator.
 16. The system ofclaim 11, wherein the mode logic is operable to: operate the motor inopen-loop control in the first control mode; and operate the motor inclosed-loop control in the second control mode.
 17. The system of claim11, wherein the mode logic is operable to: operate the motor in a firstclosed-loop control in the first control mode; and operate the motor ina second closed-loop control in the second control mode.
 18. A device,comprising: pattern detection logic configured to: receive a signalgenerated by a motor having a plurality of commutation states andoperating in a first control mode; compare the signal in a number of theplurality of commutation states with a predetermined signal pattern;based on the comparison, increment a count value; and in response to thecount value exceeding a count threshold, selecting a second control modeto operate the motor.
 19. The device of claim 18, wherein: the countvalue is increased in response to the signal matching the predeterminedsignal pattern over a set of the plurality of commutation states. 20.The device of claim 18, wherein: the count threshold is selected fromone of a default value and a programmable value.